Give the jalapenos a rinse and then cut into 1/4 inch slices. Peel the carrots and cut into 1/4 inch slices.
Peel and quarter the onion, chopping into thin slices. Peel and roughly chop the garlic.
Heat a glug of oil in a medium sized sauce pan over medium heat. Saute the onion and garlic for a few minutes.
Add the spices: 1/2 teaspoon cumin seeds, 1/2 teaspoon Mexican oregano, 8-10 black peppercorns. I usually give the spices a quick crush in the molcajete but this is optional. And feel free to use powdered spices if you don't have seeds or peppercorns on hand.
Add the jalapenos and carrots. Briefly saute and then add 1.5 cups white vinegar, 1 cup water, 1 tablespoon kosher or sea salt, and 1 bay leaf (optional). Simmer until the jalapenos are just turning army green in color.
Fill two pint-sized Mason jars with the veggies and fill to the brim with the vinegar mixture. You can also use a single quart-sized Mason jar. You can give them a taste test now for a preview, but they won't have full flavor until they rest overnight in the brine.
I usually let the jars cool on the counter for a bit, then cap and store in the fridge where they will keep for weeks at a time.